VITAMIN B12: A VEGAN NUTRITION PRIMER

There’s no doubt about it: Vitamin B12 is the big issue in vegan nutrition. It’s not that it’s difficult to get enough; in fact, it’s quite easy. But this is an area where vegans absolutely need to supplement. And the consequences of not doing so can be serious.

B12 Deficiency

Vitamin B12 is needed for production of DNA (and therefore for cell division) and for maintaining nerve cells.

Two symptoms of B12 deficiency are:

Megaloblastic anemia, in which red blood cells become abnormally large because they can’t divide.

Nerve damage, which can result in a host of problems—everything from depression and mental confusion to tingling and numbness in extremities to a loss of balance and even paralysis.

The anemia is reversible with vitamin B12 therapy. The nerve damage is usually reversible, but not always.

Although anemia usually occurs first, this isn’t always the case. One problem is that another B vitamin, folate, can “mask” anemia due to B12 deficiency. Folate steps in and prevents anemia, but it can’t prevent nerve damage. So, if your diet is rich in folate but low in vitamin B12, nerve damage can actually be the first symptom of a B12 deficiency. This is a concern for vegans in particular, because our diets are often high in folate which is abundant in leafy greens and beans.

A blood level of vitamin B12 above 200 pg/ml (picograms per milliliter) is good enough to prevent anemia and nerve damage. But levels need to be above 400 pg/ml for optimal health. Vitamin B12 levels in this marginal range—200 to 400 pg/ml—are associated with high levels of a compound called homocysteine. (1)

Elevated homocysteine may be related to poorer cognitive function in older people (2, 3) and maybe also to poorer bone health. (4) Higher homocysteine levels have also been linked to risk for cardiovascular disease, although evidence for that relationship has been challenged. (5, 6)

Sources of Vitamin B12

All animal foods provide vitamin B12, which comes from bacteria in the animal’s intestines or from their diet. To the best of our knowledge, this vitamin doesn’t occur naturally in any plants. Some books and websites claim that plants like sea vegetables, shiitake mushrooms, and tempeh are sources of vitamin B12. However, many of them contain inactive B12 analogs—compounds that are similar to vitamin B12 but don’t have any vitamin activity. And no plant food has been shown to improve vitamin B12 status in humans. (7-9) Depending on any of these foods for vitamin B12 will raise your risk for deficiency.

There are only two reliable sources of vitamin B12 for vegans: foods fortified with this nutrient (which includes nutritional yeast grown on a B12-rich medium) and supplements.

Meeting Vitamin B12 Needs

The RDA for vitamin B12 is 2.4 mcg per day. But 4 to 7 mcg may be a better recommendation for preventing all potential deficiency symptoms, including elevated homocysteine. (10)

Figuring out appropriate dosages of B12 gets tricky, though, because of the way this vitamin is absorbed. Small amounts of vitamin B12 attach to receptors for absorption. These receptors quickly become saturated by just 1 to 2 mcg of vitamin B12 and they stay that way for several hours. This is the amount of vitamin B12 you might expect to get from a single meal that includes animal products or fortified foods.

If you ingest a big dose of vitamin B12 from a supplement you can still absorb a little bit of the excess that can’t attach to receptors. But absorption of that extra amount is just a very small percentage of the total. (11)

You can meet needs from several small servings of vitamin B12 consumed throughout the day. (12) This is the way omnivores typically get their B12 and we can do the same by using fortified foods. But if you’re getting all of your B12 at once—from a daily supplement—you need a lot more since absorption rates—as an overall percentage—are so low.

Here are three ways to meet vitamin B12 needs. They all refer to cyanocobalamin and I’ll explain the rationale for this below. (For recommendations for children see this chart.)

Eat two servings per day of foods fortified with at least 2 to 3.5 mcg of vitamin B12 each. You’ll need to eat these servings at least 4 hours apart to allow for optimal absorption.

Take a daily supplement providing 25 to 100 mcg of vitamin B12

Take a supplement providing 1,000 mcg of vitamin B12 twice per week

Cyanocobalamin versus Methylcobalamin

Cyanocobalamin is currently the form of vitamin B12 that is recommended by vegan nutrition experts.(13-15) People often wonder why this is, especially since cyanocobalamin has to be converted to methylcobalamin before it can do its job. Why not just take methylcobalamin directly, a form that is widely available in supplements?

It’s not because cyanocobalamin is “better.” It’s simply because it’s been well-studied and we have more reliable information about appropriate dosages.

Methylcobalamin is thought to be less stable and it seems that much, much higher doses are required to protect B12 status. We don’t really have good information that allows us to be specific about those doses, so it seems safest to stick with cyanocobalamin. And unless you smoke or have kidney disease, your body easily converts cyanocobalamin to the active methylcobalamin.

While there is a little bit of cyanide in cyanocobalamin supplements (it’s there to stabilize the B12), it’s a small inconsequential amount compared to what occurs naturally in the diet. According to a study in Norway, average cyanide intake is about 95 mcg per day.(16) A twice weekly supplement of 1,000 mcg of cyanocobalamin would provide about 6 mcg per day. So even those who regularly use cyanocobalamin will have intakes that are far below the minimal risk level which is set at 3,175 mcg per day. (16)

For those who prefer to take methylcobalamin, it’s likely that 1,500 mcg per day would meet needs. (17) But again, it’s difficult to make specific recommendations about this.

Do You Really Need to Supplement?

Our need for vitamin B12 is small, and our bodies have some pretty brilliant ways to conserve this nutrient and can also store substantial amounts of it. We have bacteria living in our guts that produce B12, too. So do we really need to supplement?

The answer—as you can probably guess—is yes. Vegans who don’t supplement with B12 can expect to eventually develop a deficiency. How quickly that happens is something that just can’t be predicted. Some people have large stores; some don’t. And we are not able to absorb the B12 that is produced in our own guts since most of it is produced too far from the site of absorption. There is also no evidence that saliva provides active vitamin B12. (18)

For More Information

This blog post has some tips for finding vegan vitamin B12 supplements. (The information is current as of February, 2015)

For more information about vitamin B12, please refer to chapter 3 in Vegan for Life.

And for a comprehensive overview of vitamin B12 nutrition with all pertinent research, the best resource comes from vegan vitamin B12 guru Jack Norris, RD on his Vegan Health website.

Opinion of the Scientific Panel on Food Additives, Flavourings, Processing Aids and Materials in Contact with Food (AFC) on hydrocyanic acid in flavourings and other food ingredients with flavouring properties. The EFSA Journal (2004) 105.